1. Field of the Invention
The present invention relates to a polyphenylene ether resin composition superior in impact resistance, heat resistance, mechanical strength, moldability, and flow properties, and more particularly, to such a composition composed of a polyphenylene ether resin, a polystyrene resin, and a specific polyorganosiloxane-based graft copolymer.
2. Description of the Prior Art
Applications of polyphenylene ether resins as engineering plastics are expanding since these resins are superior in heat resistance, stiffness, etc. However, the applications are restricted in that these resins are somewhat inferior in impact resistance.
For improving polyphenylene ether resins in impact resistance, methods comprising blending them with polybutadiene elastomers are disclosed in Japanese Patent Publication No. 32731/72, Japanese Patent Application Kokai (Laid-Open) No. 2345/71, and other documents. According to these methods, however, none of practically useful blends superior in heat stability can be obtained, because unsaturated bonds remain in the blended polybutadiene elastomers and this makes the blends thermally instable.
On the other hand, methods for improving polyphenylene ether resins in moldability or processability as well as in impact resistance are disclosed in U.S. Patent No. 3,361,851, Japanese Patent Publication No. 7069/67, etc. These methods comprise blending polyphenylene ether resins with polyolefins such as ethylene-propylene copolymers. According to these methods, however, the low compatibility of polyphenylene ether resins with the polyolefin may cause delamination in molded products of the blend containing 10% by weight or more of the polyolefin. Moreover, the surface appearance of such molded products is inferior and the improvement of impact resistance is not much remarkable.
Further, Japanese Patent Application Kokai No. 75663/74 discloses a polyphenylene ether resin composition improved in moldability or processability while retaining the stiffness and mechanical strength of polyphenylene ether resins. This composition is a product of improving the above polyolefin blending method, that is, a product of blending a polyphenylene ether resin with a polyolefin-based graft copolymer resulting from the graft polymerization of a styrene monomer onto a polyolefin. However, the impact resistance is not sufficiently enhanced according to this method.